A mobile radio network covers a geographical area which is divided into cell areas, wherein each cell area is generally served by a radio network node. A radio network node may be a Radio Base Station (RBS), also sometimes referred to as e.g. “eNB”, “eNodeB”, or BTS (Base Transceiver Station). A radio network node or RBS may provide radio coverage to one or more cells. The radio network nodes communicate with user equipments (UEs) also referred to as mobile stations, mobile terminals, wireless terminals, mobile telephones, cellular telephones or smart phones situated within its radio network cell. Other examples of UEs are laptops, notebooks, tablets and handheld devices. All of those having wireless communication capabilities. In addition, a radio mobile communication may be performed between two or more UEs, two or more radio network nodes or two or more radio network core nodes. All of the above-mentioned pieces form part of a radio mobile network.
When the communication is performed between two user equipments, each of these equipments communicates within a frequency band or channel allocated to one operator in a radio network. The frequency band may be a whole spectrum chunk whilst a channel may be a subset of the spectrum resources of the frequency band used for resource management purposes.
Furthermore, the frequency bands in Long Term Evolution (LTE) may operate in both paired and unpaired spectrum, requiring flexibility in the duplex arrangement.
The LTE-system has a Physical Uplink Control Channel (PUCCH) which is used to carry the Layer 1 and Layer 2 (L1/L2) control information. The transmitted control information is mainly a periodic channel state report e.g. Channel Quality Indicator, CQI, a hybrid-ARQ (Automatic Repeat Request) acknowledgement ACK/non-acknowledgement NACK) corresponding to the downlink transmission or a scheduling request (SR). Different information needs different number of bits and different PUCCH formats are defined to classify those. In this application, we focus on the scheduling request, SR, on PUCCH.
The scheduling request, SR, is a request from a user equipment, UE, to a Radio Base Station (RBS) to be allocated resources for uplink communication. The RBS receives the SR and identifies which UE the SR belongs to. This is possible because each of the UEs is allocated a static and unique PUCCH SR resource which is configured by RBS. FIG. 1 shows an allocated PUCCH SR resource for a UE.
The scheduler in an RBS needs to be aware of the queue status in each UE in order to perform an adequate scheduling in the uplink, i.e. in the direction from the UE to the RBS. For this reason, a “UE send buffer status report” is transmitted to the RBS to inform about the send buffer status. In order to transmit the buffer status report, a SR is sent/triggered by the UE, in order to ask for an UL scheduling resource. Consequently, a SR is transmitted by the UE on a SR resource (on the PUCCH) selected by the RBS when a buffer status report is to be sent, e.g., when new data have arrived to a previously empty UE buffer, or when newly arrived data have higher priority than the existing data stored in the UE buffer.
The amount of SRs generated or triggered by each UE is very dependent on the characteristic of different types of traffic. One type of traffic that triggers lots of SRs is Voice over IP (VoIP), where small amounts of data arrive frequently Moreover, VoIP has high priority and is to be scheduled quickly after the data arrives. Since the data arrival time is short, the UE buffer may already be empty when the next VoIP packet arrives.
As standardized, the SRs are to be transmitted on the PUCCH and only one PUCCH SR resource is allocated. However, when a UE is not allocated any PUCCH resource, e.g. due to that the number of users exceeds the PUCCH SR capacity, the SRs may still be transmitted but on the contention based Random Access Channel (RA-SR). In practice, it is desired to not use RA-SR too often, due to the higher delay and additional signaling compared with PUCCH SR.
The PUCCH SR should be unique in at least one of three dimensions, i.e. time domain, frequency domain and coding domain. SR periodicity is introduced to achieve the time domain SR multiplexing, where a UE only can send SR periodically with a certain offset in time. Different UEs are able to send SRs on different resource blocks (RB) pairs or with different coded sequences resulting in the frequency domain and coding domain multiplexing. The different coded sequence refers to different orthogonal sequences or cyclic shifts. If the three domains are multiplexed, the capacity of the PUCCH SR is highly improved and a large number of UEs obtain their own unique PUCCH SRs. In total, there are a maximum of 36 code sequences for PUCCH SRs in one RB pair, which means that a maximum of 36 UEs can send SRs at the same time with the same RB pair.
PUCCH SRs are orthogonal within a cell, which entails that no intra-cell interference is generated. However, the inter-cell SR interference is significant when users belonging to different cells are transmitting SRs at the same time using the same resource block (RB). When the inter-cell SR interference increases, the number of errors related to SR detection in the RBS increases as well, and network performance decreases.
Further, the mere allocation of one PUCCH SR does not necessarily mean that PUCCH SR interference is generated. This is because the interference will only be generated when the PUCCH SR resource is utilized, i.e. when an SR is sent. As previously explained, the SR is triggered only for uplink data transmission and different types of users/UEs will generate a different amount of SRs.